Aluminum-tin base bearing alloy and composite

ABSTRACT

An aluminum-tin (Al-Sn) base bearing alloy and a bearing material which is made by applying the Al-Sn base bearing alloy to a backing steel sheet by pressure welding. The Al-Sn base bearing alloy of the invention is characterized in that the coarsening of tin particles and the lowering of the hardness under high temperature conditions are quite small so that the wear resistance as well as the fatigue strength of the alloy are quite excellent. The Al-Sn base bearing alloy comprises 3.0-35 wt. % of Sn; at least 0.1 wt. % of Cr; at least 1.0 wt. % of Zr, with the proviso that the total amount of Cr and Zr is not more than 10 wt. %; and the remainder of aluminum. The Al-Sn base bearing alloy of the invention can further contain 3 wt. % or less in total of Cu and/or Mg and 9 wt. % or less in total of one or more members of Pb, Bi, In, Tl and Cd, thereby improving the bearing characteristics. The wear resistance of this bearing alloy can be expected even when the shaft to be supported is hard and the shaft surface is coarse. Accordingly, a marked effect can be obtained when the bearing alloy is used for the bearing devices of internal combustion engines in which spheroidal (nodular) graphite cast iron is generally used for crank shafts.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 47,336, filed June 11, 1979, now U.S. Pat. No. 4,278,740, and application Ser. No. 136,619, filed Apr. 2, 1980, now U.S. Pat. No. 4,340,649, the entire contents of both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an aluminum-tin (Al-Sn) base bearing alloy which is prepared by adding tin to an aluminum matrix and to a bearing material which is made by applying the Al-Sn base bearing alloy to a backing steel by pressure welding. More particularly, the Al-Sn base bearing alloy of the invention is characterized in that the bearing alloy is improved in several properties thereof by adding various kinds of additive elements. That is, the fatigue strength is much improved by reducing the lowering of the hardness at high temperatures and, especially, by avoiding the coarsening of tin particles. Furthermore, the wear resistance of the bearing alloy is also raised in order to improve the durability relative to the shaft to be supported which has a hard and coarse surface. Accordingly, in the case that the bearing alloy of the present invention is used for the bearing devices around the crank shafts of internal combustion engines which require severe conditions, remarkable advantages can be expected.

(2) Description of the Prior Art

In recent years, the automobile internal combustion engines are required to be made compact and to have high power. Further, as the countermeasure to the regulation of exhaust gas, they must be provided with blow-by gas recirculation devices or the like. Therefore, the use conditions for the bearing materials in the internal combustion engines have become severe at high loads and high temperatures. Under such severe conditions, the conventional bearing materials are liable to cause fatigue failure and abnormal wearing which cause several troubles.

In connection with the shafts to be brought into engagement with the bearing materials, there is a tendency to use, in place of the hitherto produced forged shafts, less expensive shafts made of spheroidal graphite cast iron or other coarse material in order to reduce the production costs. Therefore, improvements in the wear resistance, seizure resistance and fatigue resistance at high temperatures are required.

Exemplified as the Al-Sn base alloy used for making the bearings of internal combustion engines in the prior art are: Al(remainder)--Sn(10-30)--Cr(0.1-1.0); Al(remainder)--Sn(3.5-4.5)--Si(3.5-4.5)--Cu(0.7-1.3); Al(remainder)--Sn(4-8)-Si(1-2)--Cu(0.1-2)--Ni(0.1-1); Al(remainder)--Sn(3-40)--Pb(0.1-5)--Cu(0.2-2)--Sb(0.1-3)--Si(0.2-3)--Ti(0.01-1); Al(remainder)--Sn(15-30)-Cu(0.4-2); and Al(remainder)--Sn(1-23)--Pb(1.5-9)--Cu(0.3-3)--Si(1-8), in which the values in parentheses denote the percentages by weight of the component materials.

When these conventional alloys are used for the bearings of automobile internal combustion engines under severe conditions as described above, fatigue failure is sometimes caused to occur in a short time if the engines are continuously operated under heavy loads. This is considered to be due to the fact that the temperature of the lubricant oil in an internal combustion engine becomes very high during the continuous full-load running thereof, for example, the temperature of the lubricant oil in an oil pan reaches 130° C.-150° C., so that the temperature of the sliding surfaces of bearings also becomes very high. As the result, since the eutectic point of such alloy is about 225° C. or so, the hardness of the alloy rapidly becomes low under the high temperature conditions, which causes fusion and migration of the Sn component and the fatigue strength is resultantly lowered. The inventors of the present invention have prepared an alloy, the hardness of which is not lowered at high temperatures and the Sn component of the alloy is hardly altered. The alloy was worked into the shapes of bearings for internal combustion engines and they were subjected to fatigue tests under dynamic loads at high oil temperatures. As a result, the improvement in fatigue strength was recognized, which substantiated the above-mentioned consideration.

Further, in addition to the lowering of the fatigue strength due to the loss of hardness at high temperatures as mentioned above, the coarsening of tin particles in the texture of conventional Al-Sn alloy also causes lowering of the fatigue strength. That is, the aluminum bearing material is generally formed by applying Al-Sn alloy to a backing steel through pressure welding, in which an annealing step is required after the pressure welding in order to improve the adhesive strength between both metals. The annealing is generally done at a temperature below the point at which an Al-Fe intermetallic compound deposits and the higher the treating temperature is and the longer the treating time is, the larger the adhesion strength becomes. As a matter of fact, when the conventional Al-Sn alloy is placed in a high temperature condition during annealing, the coarsening of aluminum grain boundaries and tin particles is disadvantageously caused to occur in the alloy texture. That is, when the conventional aluminum bearing alloy is subjected to annealing in order to improve the adhesive strength to the backing steel, the coarsening of tin particles is brought about, which results in the lowering of the fatigue strength of the Al-Sn alloy at high temperatures.

Further, these conventional Al-Sn bearing alloys are not good enough in wear resistance. Especially, when shafts having hard and coarse surfaces such as those made of spheroidal graphite cast iron are brought into engagement with the bearing alloys, the wear resistance is greatly lowered and fatigue failures are liable to occur, which has been a serious problem in the prior art.

BRIEF SUMMARY OF THE INVENTION

Accordingly, in order to eliminate one or more of the above-described disadvantages in the conventional Al-Sn base bearing alloy, the primary object of the present invention is to provide an Al-Sn base bearing alloy which exhibits a small lowering of hardness at high temperatures, and as a result, has a relatively high fatigue strength.

Another object of the present invention is to provide an improved Al-Sn base bearing alloy in which the coarsening of tin particles is not caused to occur during the annealing step or during the use under high temperature conditions, which results in a higher fatigue strength.

A further object of the present invention is to provide an Al-Sn base bearing alloy having a high wear resistance, especially a bearing alloy exhibiting a high wear resistance to shafts which are made of hard and coarse materials such as spheroidal graphite cast iron that is used for making the crank shafts of internal combustion engines.

Still a further object of the present invention is to provide a bearing material which is made by applying the above bearing alloy to the surface of a backing steel sheet and bearing devices for internal combustion engines which are made of the above bearing material.

According to the present invention, the Al-Sn base bearing alloy basically comprises 3.0-35 wt. % of Sn; at least 0.1 wt. % of Cr and at least 1.0 wt. % of Zr, with the proviso that the sum of Cr and Zr is not more than 10 wt. %; and the remainder of aluminum. In order to improve the bearing characteristics, the Al-Sn base bearing alloy of the invention can further contain up to 3 wt. %, in total, of Cu and/or Mg, and/or up to 9 wt. %, in total, of one or more members of Pb, Bi, Tl, Cd and In. In connection with the above additives, the addition of at least 0.1 wt. % of Cr and at least 1.0 wt. % of Zr, with the proviso that the sum of Cr and Zr is not more than 10 wt. %, is effective especially in the prevention of the lowering of the hardness at high temperatures, in the prevention of the coarsening of Sn particles and in increasing the load at seizure when the bearing is in contact with a spheroidal graphite cast iron shaft. Further, it is considered that the specified additive group exhibits a notable effect in improving the wear resistance.

According to the present invention, a first Al-Sn base bearing alloy consists essentially of 3.5-35, especially 7.5-25, wt. % of Sn; 0.1-1.0, especially 0.1-0.7, wt. % of Cr; 1-10, especially 1-6, wt. % of Zr; up to 3.0, especially 0.1-2.0, wt. % of Cu and/or Mg; and up to 9.0, especially 0.5-5.0 wt. % of one or more members selected from the group consisting of Pb, Bi and In.

A second Al-Sn base bearing alloy, according to the present invention, consists essentially of 3-7% by weight of Sn; 0.1 to 1.0% by weight of Cr; from 1-10% by weight of Zr; 0.1-0.8% by weight in total of Cu and/or Mg; 0-9% by weight in total of one or more constituents selected from the group consisting of Pb, Bi, Tl, Cd and In; and the remainder is Al.

A third Al-Sn base bearing alloy, according to the present invention, consists essentially of 3-35%, preferably 7-35%, by weight of Sn; 1-10% by weight in total of Cr and Zr with the proviso that the alloy contains at least 1% by weight of Cr and at least 1% by weight of Zr; 0-3% by weight in total of Cu and/or Mg; 0-9% by weight in total of one or more constituents selected from the group consisting of Pb, Bi, Tl, Cd and In; and the remainder is Al.

A fourth Al-Sn base bearing alloy, according to the present invention, consists essentially of 3-7% by weight of Sn; 1-10% by weight in total of Cr and Zr with the proviso that the alloy contains at least 1% by weight of Cr and at least 1% by weight of Zr; 0.1-0.8% by weight in total of Cu and/or Mg; from 0-9% by weight in total of one or more constituents selected from the group consisting of Pb, Bi, Tl, Cd and In; and the balance is Al.

DETAILED DESCRIPTION OF THE INVENTION

The Al-Sn base bearing alloy of the present invention is prepared by adding the above-mentioned Sn, Cr, Zr, and, optionally, one or more members of the foregoing specified additive groups to the matrix of aluminum.

Though the tin is added for the main purpose of lubrication, the reason why the content of tin is restricted to the range of 3.0 to 35 wt. %, preferably 3.5 to 35 wt. %, especially at least 7.5 wt. %, depends upon the fact that the addition of tin in an amount of more than 35 wt. % improves the conformability and low friction property. However, it reduces the hardness of the bearing alloy. When the quantity of tin is less than 3.0, preferably 3.5 wt. %, on the contrary, the bearing alloy becomes too hard and is insufficient in view of the conformability or the like. According to the prior art, the upper limit of the amount of tin has been regarded as being about 15% to the Al-Sn alloy so as to separately disperse tin particles, because it has been considered that, when more than 15% of tin is contained, the tin particles in the aluminum matrix cannot exist in a separated state but rather they exist in a continuous state and the hardness under high temperature conditions becomes low. In the present invention, however, the addition of tin up to 35 wt. % has been made possible without any practical disadvantage, by the effect of the addition of the other elements. The addition quantity of tin in the range of 3.0 to 35 wt. % can be determined properly in compliance with expected uses. Generally speaking, the addition quantity of tin is made small when a bearing receives a large load, while for light duty purposes, much tin can be added to the bearing alloy. In another viewpoint, when there is fear of seizure, the addition quantity of tin may be increased, while if there is no fear of seizure, the quantity of tin may be reduced. However, in recent cases, the temperature of a bearing often becomes high due to the high temperature oil and this causes the deformation of the bearing which is followed by the occurrence of seizure and fatigue. Therefore, the addition quantity of tin may be determined from the viewpoint to reduce the deformation at high temperatures.

The addition of chromium (Cr) is effective in that the hardness of the alloy is raised to prevent the alloy from softening at high temperatures and thus the coarsening of tin particles is not caused to occur even in annealing. In the first place, the effects to raise the hardness and to avoid the softening of alloy at high temperatures will be described. When the quantity of chromium is less than 0.1 wt. %, the improvement in high temperature hardness cannot be expected. More particularly in connection with the improvement in the high temperature hardness, the chromium forms a solid solution in aluminum which raises the recrystallization temperature of aluminum and, in addition, the solid solution itself improves the hardness of the aluminum matrix. At the same time, the hardness of the alloy containing chromium becomes higher even when it is subjected to rolling several times which is contrasted to casting. With the rise of the recrystallizing temperature of aluminum, the bearings of engines that are exposed to high temperatures can maintain their mechanical properties. Especially, the lowering of hardness at high temperatures can be reduced and the softening of bearings in a high temperature range can well be avoided, thereby improving the durability of bearings. Further, the Al-Cr intermetallic compound that is deposited over the limit of solid solution, has a Vickers hardness of more than about 370 so that the dispersion of such a compound aids the bearing alloy in maintaining the hardness at high temperature. Therefore, the dispersion of such an intermetallic compound in a proper quantity gives a good effect. The preferable range of the quantity of chromium is, as described above, 0.1 to 1.0 wt. %, and if the quantity of chromium is within such a range, fine and uniform deposition of the intermetallic compound is formed and it increases the hardness of the bearing alloy.

The effect of the addition of chromium to avoid the coarsening of tin particles will be described in the following. The coarsening of tin particles is a phenomenon owing to the migration of aluminum grain boundaries and tin particles in a high temperature condition of the Al-Sn alloy. Since the chromium is precipitated as the above-mentioned Al-Cr intermetallic compound which is finely dispersed in the aluminum alloy matrix, this intermetallic compound inhibits directly the migration of aluminum grain boundaries and, at the same time, it obstructs the growth of aluminum crystal grains. Therefore, the migration of tin particles is also hindered and, as the result, the coarsening of tin particles can be avoided. This is related to the fact that the finely divided tin particles are retained as they stand during the repetitions of rolling and annealing, and the above-described various effects can be obtained. Such phenomenon can be observed when the quantity of tin is small, however, the effect becomes larger when the quantity of tin is relatively large (more than about 10 wt. %). Especially, in the case that the quantity of tin exceeds about 15 wt. % in which the tin particles exist in a continued state, the effect of the addition becomes notable. Further, even when the quantity of tin is less than 10 wt. %, the effect of addition of chromium is, of course, expected sufficiently according to use conditions and utilities of the alloy.

Furthermore, the liquidation of tin particles having a low melting point of about 232° C. can be prevented effectively under high temperature conditions because the tin particles are well maintained in a finely divided state in the aluminum matrix. From this viewpoint, the effect of the prevention of lowering in hardness will be understood.

In the above passage, the effect for preventing the coarsening of tin particles in the annealing step is described. This effect can also be expected in the working condition of the bearing material in which the temperature is equal to the annealing condition. Accordingly, the fatigue strength in practical uses can also be improved with the inhibition of softening.

In order to improve mainly the wear resistance, it is effective to use at least 0.1 wt. % of chromium and at least 1.0 wt. % of zirconium, with the proviso that the sum of chromium and zirconium is not more than 10 wt. % and preferably in the range of 1.1 to 6.1 wt. %, which quantity may be determined in accordance with the purpose of use. The reason for the above restriction is as follows. The precipitated substances (or crystallized substances, the same shall apply hereinafter) of these elements are dispersed in the aluminum matrix, therefore, the wear resistance can be improved. If the addition quantity of the specified additives is less than 1.1 wt. % in total, the effect of the addition of chromium and zirconium cannot be exhibited. On the contrary, if the addition quantity of these two elements is more than 10 wt. %, the precipitated substances become too much, so that the adaptability to rolling becomes worse and the repeating of rolling and annealing becomes difficult. Further, the formation of the fine particles of tin is inhibited. In order to eliminate these undesirable effects completely, the preferable upper limit is made 6 wt. % or so.

The forms of precipitation of chromium and zirconium are the precipitated substance of chromium and zirconium, those of intermetallic compounds between the added elements, those of intermetallic compounds of aluminum and added elements, and those of intermetallic compounds of aluminum and the intermetallic compound of added elements. The wear resistance can be improved by the precipitated substances in any forms of the above.

The Vickers hardnesses of these precipitated substances reach several hundreds, so that the precipitated substances are very hard and the wearing of bearings caused by the friction with shafts can be reduced notably by the precipitated substances. Accordingly, a quite good result can be obtained when a proper quantity of the precipitated substance exists in the aluminum matrix. The range of the proper quantity of chromium and zirconium is 1.1 to 10 wt. % as described above, and if the quantity of the precipitated substance is in this range, the precipitated substance can be dispersed uniformly and the wear resistance can effectively be improved without causing any ill effects such as the lowering of conformability.

The effect to improve the wear resistance is remarkable when the bearing supports a shaft having a hard and coarse surface. The performance of a bearing generally depends upon the hardness and coarseness of the material to be supported to a great extent. For example, when the conventional Al-Sn base bearing material is used for supporting a shaft made of spheroidal graphite cast iron, the properties of the bearing such as antiseizing property and wear resistance are markedly lowered. Since the shafts made of spheroidal graphite cast iron can be produced at low cost, such shafts have been widely employed recently in place of steel shafts. In the iron matrix of the shaft, soft graphite particles are scattered. Therefore, when the shaft surface is scraped, blade-like grinding burrs are formed around the particles of graphite. When the shaft having such grinding burrs is slid relative to the bearing under a heavy load in which the coarsenesses of the shaft and the bearing and the thickness of the oil film between them are equal to each other, the bearing surface which is softer than the shaft is ground. If such condition is continued, the surface of the bearing becomes coarse and the clearance between the bearing and the shaft becomes large, which causes the breakage of the oil film or the lack of an oil film. As a result, the direct contact between the shaft and the bearing (the metal-to-metal contact) is caused to occur, which results in the occurrence of seizure of both the parts.

While, in the alloy according to the present invention, the precipitated substance which is formed in the aluminum matrix by the addition of 1.1 to 10 wt. %, in total, of chromium and zirconium, is harder than the above-mentioned grinding burrs of the shaft of spheroidal graphite cast iron. Therefore, the precipitated substance removes the above-mentioned grinding burrs from the surface of the shaft and, in addition, the metal transfer and adhesion of the precipitated substance is hard to occur. Therefore, the course of wearing of the bearing surface can be suppressed within a relatively short time to cause the formation of a stable oil film. As a result, in relation to the shaft made of the spheroidal graphite cast iron, the wear resistance and the antiseizing property of the bearing can be improved.

In addition to the above-described compositions of the present invention, the bearing alloy can further contain zero to 3 wt. % of copper (Cu) and/or magnesium (Mg). The copper and/or magnesium are added in view of the fact that they reduce the lowering of the hardness at high temperatures. The preferable range of the addition of them is 0.1 to 2.0 wt. %. When the addition quantity of them is less than 0.1 wt. %, the rise of hardness cannot be expected so much, while if the addition quantity is more than 3.0 wt. %, the alloy becomes too hard to reduce the rolling property and the anticorrosiveness is lowered. Further, with regard to the magnesium, the addition of more than 3 wt. % increases the hardness, however, the rise in hardness during the roll working becomes too large, therefore, satisfactory rolling cannot be performed and it becomes difficult to obtain a quite fine tin texture. Furthermore, the magnesium existing as a solid solution in the aluminum matrix is liable to deposit during the annealing. Therefore, the reinforcing of the aluminum matrix by the solid solution cannot be expected owing to the deposition of the excess magnesium. Therefore, the preferable ratio of addition is not more than 2.0 wt. %. Further, the effect of the addition of copper and/or magnesium is exhibited when the chromium is added simultaneously, and the effect to raise the hardness at high temperatures cannot be expected when only the copper and/or magnesium are added. In other words, if copper and/or magnesium are added to the aluminum matrix, the hardness in the rolling is much raised, which is remarkable as compared with the case in which other elements are added to the aluminum matrix. It is to be noted, however, that the aluminum matrix containing the copper and/or magnesium is easily softened at about 200° C. Therefore, it cannot be expected to maintain the hardness at high temperatures. On the contrary, when the copper and/or magnesium are added together with the chromium, the hardness which is raised during the rolling by the effect of the addition of the copper and/or magnesium is not so much lowered by the annealing, which is brought about by the addition of the chromium. This hardness can be maintained under high temperature conditions. Therefore, as compared with the prior art alloys, the bearing alloy of the present invention has a higher hardness at high temperatures, which results in an improvement in the fatigue strength. When the copper and magnesium are simultaneously added, it is desirable that the total quantity of them is not more than 3 wt. %, while the quantity of copper itself is not more than 2 wt. %.

In the second and fourth alloys of the invention, there is contained from 0.1 to 0.8 wt. % in total of copper (Cu) and/or magnesium (Mg), in view of the low amounts of tin (Sn), i.e., from 3 to 7 wt. %, used in the second and fourth alloys of the invention.

Further, in the bearing alloy of the present invention, the property as a slidable metal containing tin can be further improved by adding zero to 9 wt. %, preferably 0.5 to 5.0 wt. %, in total of one or more members selected from the group consisting of lead (Pb), bismuth (Bi), indium (In), thallium (Tl) and cadmium (Cd). The effect of the addition of lead, bismuth, indium, thallium and cadmium is exhibited when they are added together with chromium and zirconium. In the prior art, it has been considered that these elements are added to Al-Sn base alloys and the addition has been practiced in some cases. However, when only these elements are added to the Al-Sn base alloy, they form alloys so that the disadvantage that the melting point of tin becomes low cannot be avoided. Thus, the fusion and the migration of tin at low temperatures is liable to occur in the prior art Al-Sn base alloy, which causes the growth of tin particles into larger and coarse ones. When such alloy is employed as a bearing material, partial fusion and scraping are caused to occur under continuous heavy load running. On the contrary, the tin particles are made fine by the addition of chromium and zirconium and such texture is maintained at high temperatures in the bearing alloy of the present invention. Therefore, even when one or more of the above lead, bismuth, indium, thallium and cadmium are added to the alloy, the lubricating property of tin can be improved without causing the above troubles in the prior art. Further, the bearing alloy of the invention can be used for the bearing in which a high fatigue strength is required. In addition, it becomes possible to improve the conformability of the bearing material. As described above, the addition quantity of one or more of the lead, bismuth, indium, thallium or cadmium having the above effects is in the range of up to 9 wt. % in total. Among these elements, lead and indium are most preferable which are followed by bismuth and cadmium, and then thallium. This depends upon the fact that lead and indium are most flowable under pressure so that the sliding property and conformability become good. The next, bismuth and cadmium, are somewhat harder and higher in melting points as compared with the lead and indium. The last, thallium, has similar properties as those of lead and indium. However, the production quantity of thallium is small and it is expensive. Further, it is desirable that the total addition quantity of lead, bismuth, indium, thallium, cadmium and tin is not more than 35 wt. %. Further, one or more of lead, bismuth, indium, thallium and cadmium can be added together with the above-mentioned copper and/or magnesium, in which the lowering of the high temperature hardness can be reduced. At the same time, the lubricating property of tin can be improved.

The above-described Al-Sn base bearing alloy is mainly used as the sliding bearings of automobile internal combustion engines or the like, in which the bearing alloy is generally applied to backing steel sheets by pressure welding and, in order to increase the adhesive strength, the annealing is done after the pressure welding. However, in the prior art Al-Sn base alloys, the lowering of the hardness, the fusion of tin particles and so forth are caused to occur because the migration of aluminum grain boundaries and tin particles in the alloy texture is brought about which causes the coarsening of the tin particles. While in the present invention, the migration of aluminum grain boundaries and the growth of aluminum crystal particles are effectively avoided by the precipitated substance of Al-Cr intermetallic compound which is generated in the pressure welding and annealing steps. Therefore, the bearing alloy of the present invention is free from the above ill influences of annealing and, as a result, the adhesion strength between the Al-Sn base alloy and backing steel sheets can be made high by raising the temperature of annealing. Since the above fact can be applied to the case in which the bearing alloy of the present invention is placed under the circumstances which correspond to the temperature of annealing, it is quite meaningful that the fatigue strength can be improved by the prevention of softening. Furthermore, the improvement in the wear resistance is also observed. Especially, the bearing alloy is quite effective when it is used for the shafts made of spheroidal graphite cast iron.

With taking all the properties into consideration such as the adaptability to casting and rolling, the adhesiveness to the backing steel sheet, the workability, the antiseizing property, the wear resistance and the sliding characteristic, the most preferable composition of the bearing alloy of the present invention is 7.5-25 wt. % of Sn; 0.1-0.7 wt. % of Cr; 1.0-6.0 wt. % of Zr; 0.1-2.0 wt. % of Cu and/or Mg; 0.5-5.0 wt. % of Pb, Bi and/or In; and the remainder of Al. When the above elements of Pb, Bi and/or In are not added, the quantity of Sn may be increased to 10-30 wt. %. Further, the addition of Cu and/or Mg can be omitted.

In the following, the present invention will be described further in detail by several examples.

The following Table A shows the compositions of the alloys (specimens) of the present invention 1-30, and comparative alloys (specimens) 101-107. This depends upon the fact that, as described above, at least 0.1 wt. % of chromium and at least 1.0 wt. % of Zr are indispensable components for the alloy of the present invention, with the proviso that the sum of Cr and Zr is not more than 10 wt. %.

In the preparation of the alloys 1 to 30, an aluminum material was melted in a gas furnace and, in accordance with the formulae of Table A, Al-Cr, Al-Zr, Al-Cu and Al-Mg base alloys were dissolved into the molten aluminum, respectively. After that, Sn and Pb, Bi and In were added and degassing was performed. Then, metal mold casting was performed, which was followed by repeated rolling and annealing (350° C.) to obtain specimens. The high temperature hardnesses of the specimens were then measured. In the next step, these specimens were subjected to rolling and after that, the alloy specimens were fixed to backing steel sheets by pressure welding to obtain bimetallic specimens. These were then subjected to annealing and worked into plain bearings.

In Table A, the results of seizing load tests are shown, which tests were carried out by using an ultrahigh pressure seizure tester. In the tests, an 18 mmφ test piece (surface coarseness: 0.9-1.1 μm) was pressed against a rotary disk at a sliding velocity of 468 m/min. In one test, the rotary disk was made of steel (S 50C) having a surface coarseness of 0.3 to 0.8 μm and a hardness Hv of 500-600. In another test, the rotary disk was made of spheroidal graphite cast iron (DCI) (surface coarseness: 1.0 μm, hardness: Hv 200-300). The loads when seizure occurred were measured. The loads applied in the test were increased 50 Kg/cm² at 20 minute intervals. As the lubricant, SAE 10W30 motor oil (temperature: 140°±5° C.) was used under forced lubrication conditions. The data in Table A establishes that when the amount of Cr is at least 0.1 wt. % and the amount of Zr is at least 1.0 wt. %, the load at seizure is unexpectedly high when the alloy is in contact with spherical graphite cast iron (DCI).

                                      TABLE A                                      __________________________________________________________________________                                     Load at                                                                        Seizure                                        Al     Sn Cr                                                                               Zr Cu                                                                               Mg Pb                                                                               Bi In                                                                               Cd Tl                                                                               S50C                                                                              DCI                                         __________________________________________________________________________     1    bal                                                                              3.5                                                                               0.5                                                                              2.0                 550                                                                               650                                         2    ↑                                                                          10 0.2                                                                              5.0                 600                                                                               ↑                                     3    ↑                                                                          13 0.1                                                                              1                   600                                                                               600                                         4    ↑                                                                          ↑                                                                           ↑                                                                          1.1                 ↑                                                                           ↑                                     5    ↑                                                                          ↑                                                                           ↑                                                                          1.2                 ↑                                                                           650                                         6    ↑                                                                          ↑                                                                           ↑                                                                          1.5                 550                                                                               ↑                                     7    ↑                                                                          ↑                                                                           ↑                                                                          2.0                 ↑                                                                           ↑                                     8    ↑                                                                          ↑                                                                           ↑                                                                          5.0                 600                                                                               600                                         9    ↑                                                                          ↑                                                                           ↑                                                                          10.0                550                                                                               550                                         10   ↑                                                                          ↑                                                                           0.9                                                                              1.0                 ↑                                                                           650                                         11   ↑                                                                          ↑                                                                           ↑                                                                          1.1                 ↑                                                                           ↑                                     12   ↑                                                                          ↑                                                                           ↑                                                                          1.2                 ↑                                                                           ↑                                     13   ↑                                                                          ↑                                                                           ↑                                                                          1.5                 ↑                                                                           ↑                                     14   ↑                                                                          ↑                                                                           ↑                                                                          2.0                 600                                                                               ↑                                     15   ↑                                                                          ↑                                                                           ↑                                                                          5.0                 ↑                                                                           600                                         16   ↑                                                                          ↑                                                                           ↑                                                                          10.0                550                                                                               550                                         17   ↑                                                                          ↑                                                                           0.3                                                                              3.0                 ↑                                                                           650                                         18   ↑                                                                          ↑                                                                           0.6                                                                              3.0                 600                                                                               ↑                                     19   ↑                                                                          ↑                                                                           1.0                                                                              1.0                 550                                                                               650                                         20   ↑                                                                          ↑                                                                           1.0                                                                              3.0                 600                                                                               ↑                                     21   ↑                                                                          35 0.5                                                                              2.5                 750                                                                               750                                         22   ↑                                                                          20 0.5                                                                              5.0     2.0         800                                                                               850                                         23   ↑                                                                          30 0.8                                                                              7.0          0.5    750                                                                               700                                         24   ↑                                                                          10 0.3                                                                              3.0                                                                               2.0    4.0       700                                                                               800                                         25   ↑                                                                          15 0.3                                                                              3.0                                                                               0.2  3.0         850                                                                               850                                         26   ↑                                                                          15 0.1                                                                              1.5                                                                               1.0                                                                              0.3  7.0       700                                                                               700                                         27   ↑                                                                          15 0.7                                                                              2.0     1.0         700                                                                               850                                         28   ↑                                                                          20 0.5                                                                              1.0                                                                               0.5  3.0         750                                                                               750                                         29   ↑                                                                          13 1.0                                                                              3.0     3.0         600                                                                               800                                         30   ↑                                                                          35 0.5                                                                              4.0                                                                               0.5  2.0         800                                                                               850                                         31   bal                                                                              3.0                                                                               0.5                                                                              2.5                 550                                                                               650                                         32   ↑                                                                          7  0.2                                                                              2       1      2    700                                                                               850                                         33   ↑                                                                          13 0.8                                                                              4                 2 ↑                                                                           800                                         34   ↑                                                                          20 0.5                                                                              3  0.5         4    750                                                                               850                                         35   ↑                                                                          13 1 1                   550                                                                               650                                         36   ↑                                                                          ↑                                                                           ↑                                                                          2                   600                                                                               ↑                                     37   ↑                                                                          ↑                                                                           ↑                                                                          5                   ↑                                                                           600                                         38   ↑                                                                          ↑                                                                           ↑                                                                          9                   550                                                                               550                                         39   ↑                                                                          ↑                                                                           2 1                   600                                                                               650                                         40   ↑                                                                          ↑                                                                           5 ↑             ↑                                                                           600                                         41   ↑                                                                          ↑                                                                           9 ↑             550                                                                               550                                         42   ↑                                                                          3  1 2                   ↑                                                                           ↑                                     43   ↑                                                                          7  3 3                   ↑                                                                           600                                         44   ↑                                                                          13 5 4                   600                                                                               ↑                                     45   ↑                                                                          20 1.5                                                                              1.5                 ↑                                                                           650                                         46   ↑                                                                          35 2 7                   ↑                                                                           600                                         47   ↑                                                                          7  1.5                                                                              1  0.5              550                                                                               ↑                                     48   ↑                                                                          13 1 3    0.3            600                                                                               650                                         49   ↑                                                                          20 2 1  2                ↑                                                                           ↑                                     50   ↑                                                                          7  1.5                                                                              ↑ 2 7         700                                                                               750                                         51   ↑                                                                          13 1 3       1    0.5    ↑                                                                           850                                         52   ↑                                                                          20 2 1       0.5         ↑                                                                           800                                         53   ↑                                                                          7  1.5                                                                              2  0.2  3           ↑                                                                           ↑                                     54   ↑                                                                          13 1 5  0.5                                                                              0.1  5  1      750                                                                               850                                         55   ↑                                                                          20 2 1  2    2           ↑                                                                           750                                         56   ↑                                                                          5  1 4       1         1 600                                                                               650                                         57   ↑                                                                          10 2 2              2    700                                                                               800                                         58   ↑                                                                          20 5 1  0.8         5    ↑                                                                           ↑                                     101  bal                                                                              13 0.9                                                                              0.1                 700                                                                               400                                         102  ↑                                                                          13 0.1                                                                              0.9                 600                                                                               500                                         103  ↑                                                                          13 0.5                                                                              0.5                 800                                                                               250                                         104  ↑                                                                          13 0.3                                                                              0.3                 1000                                                                              150                                         105  ↑                                                                          13 0.2                                                                              0.1                 1100                                                                              100                                         106  ↑                                                                          13 1.0                                                                              --                  700                                                                               400                                         107  ↑                                                                          13 --                                                                               1.0                 600                                                                               500                                         __________________________________________________________________________

By the way, it should be noted that in the composition of the alloy of the present invention, the aluminum (Al) may of course contain a trace quantity of impurities which cannot be eliminated by the ordinary refining technique.

Although the present invention has been described in connection with preferred examples thereof, many variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein but only by the appended claims. 

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. An Al-Sn base bearing alloy, consisting essentially of from 3.0 to 35 wt. % of Sn; at least 0.1 wt. % of Cr; at least 1.0 wt. % of Zr, with the proviso that the total amount of Cr and Zr is not more than 10 wt. %; and the remainder is Al.
 2. An Al-Sn base bearing alloy, consisting essentially of: from 3.5 to 35 wt. % of Sn; from 0.1 to 1.0 wt. % of Cr; from 1 to 10 wt. % of Zr; up to 3.0 wt. % of Cu, Mg or Cu plus Mg; up to 9.0 wt. % of one or more members selected from the group consisting of Pb, Bi, In, Tl and Cd; and the remainder is Al.
 3. An Al-Sn base bearing alloy, consisting essentially of: from 7.5 to 25 wt. % of Sn; from 0.1 to 0.7 wt. % of Cr; from 1 to 6 wt. % of Zr; from 0.1 to 2.0 wt. % of Cu, Mg or CU plus Mg; from 0.5 to 5.0 wt. % of one or more members selected from the group consisting of Pb, Bi and In; and the remainder is Al.
 4. An Al-Sn base bearing alloy, consisting essentially of: from 3 to 7 wt. % of Sn; from 0.1 to 1.0 wt. % of Cr; from 1 to 10 wt. % of Zr; from 0.1 to 0.8 wt. % of Cu, Mg or Cu plus Mg; up to 9 wt. % of one or more members selected from the group consisting of Pb, Bi, Tl, Cd and In; and the remainder is Al.
 5. An Al-Sn base bearing alloy, consisting essentially of: from 3 to 35 wt. % of Sn; up to 10 wt. %, in total, of Cr and Zr, with the proviso that the alloy contains at least 1 wt. % of Cr and at least 1 wt. % of Zr; up to 9 wt. % of one or more members selected from the group consisting of Pb, Bi, Tl, Cd and In; and the remainder is Al.
 6. An Al-Sn base bearing alloy, consisting essentially of: from 3 to 7 wt. % of Sn; up to 10 wt. %, in total, of Cr and Zr, with the proviso that the alloy contains at least 1 wt. % of Cr and at least 1 wt. % of Zr; from 0.1 to 0.8 wt. % of Cu, Mg or Cu plus Mg; up to 9 wt. % of one or more members selected from the group consisting of Pb, Bi, Tl, Cd and In; and the remainder is Al.
 7. The Al-Sn base bearing alloy as claimed in claim 1, claim 2 or claim 5, containing at least 7.5 wt. % of Sn.
 8. A bearing material which is made by applying said bearing alloy as claimed in claim 1, claim 2, claim 3, claim 4, claim 5 or claim 6 to a backing steel sheet by pressure welding.
 9. The bearing alloy as claimed in claim 1, claim 2, claim 3, claim 4, claim 5 or claim 6, wherein said bearing alloy is in contact with a shaft material which is made of spheroidal graphite cast iron. 